Thermotelephone.



0. GRAETZER. THERMOTELEPHONE. APPLICATION FILED MAR. 20. 1915 Patented Am. 25, 19116..

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OTTO GRAETZER, OFBEBLIN-LICHTERFELDE, GERMANY.

THERMOTELEPHONE.

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Specification of Letters Patent.

. Patented Apr. 25, 191 6.

Application filed March 20, 1915. Serial No.-1 5,900.

tel'ephones of such kind in which a heating bodyis formed by arranging one or more Nollaston wires in a block of insulating material which block allows not only the treatment of the very thin Wollaston wires, the so-called heating-conductors, but which serves atthe same time as support for these heating-conductors in the telephone-apparatus. Although many constructions for such heating bodies are known the manufacture is still a very difficult one, especially if a great number of heating conductors is to be arranged in the same insulating block.

The object of this invention is to avoid such difficulties by providing an insulating block having an improved structure, whereby the Wollaston wires need not be mounted thereon until the block is finished. but can be placed in position on the finished block at any convenient time. The improved block has a large hole in the center and a number of" small holes near the border and a number of Wollaston wires is introduced in the center-hole and then distributed ray-like to the small holes at the border of the insulating block. When the latter has a circular shape then all wires or conductors have the same length and the same resistance between the center hole and the holes at the border of the block.

One embodiment of the invention is represented by way of example in the accompanying drawings, wherein:

Figure 1 is a vertical section and Fig. 2 is an elevation of the new heating-body for thermoaelephones.

l is an insulating-block of any insulating material ofiering resistance against any influence of acids. Such blocks are prepared by casting, pressing, punching or turning and have preferably such a shape that on the lower side an even surface is formed, whereas the upper side has an indentation 3 surrounded by a higher border 2. This insulating-bloc is provided with a central hole 4 surrounded by a border 5, which however is not so'high as the outer border '2. In this outer border is arranged in the heating-body.

' simply be dipped into a suitable a number of small holes 6, evenly distributed over the whole circumference. These holes and 6 may be produced when manufacturing the block itself, c. g.'during the casting process. they. may however also be provlded later on, c. g. by boring. Thev heating-conductors are prepared, as known by means of lVollaston wires. which, in the suitable number and twisted together into a rope or bunch 7,' are drawn through the central hole 4 of the insulating block. By ar ranging a knot 8 at the end of this bunch or by providing any other resistance, a withdrawal of the bunch is prevented. When using a knot. a loosening of-same-inay be prevented by putting on a drop of liquid solder. The upper end of the bunch, projecting from the hole 4. is untwisted and the single wires 9 are distributed in such a way that they may be conducted to and introduced in the holes 6 of the border 2. All wires have then a radial or ray-like position The ends 9'- of the wires, protruding from the lower surface of the insulating-block are bent outwardly. Before further treatment this heating body is provided with a metal-ring 10, the lower end of which projects over the lower surface of the block'so that the lower ends 9 of all wires come in direct contact with the inner surface of the metal-ring 10. Then the lower end ofthis ring 10 is dipped into liquid solder and so all wires are secured or soldered in a very simple manner to the ring. On the upper side the insulatingblock may fora short time be subjected to a heating flame, so that by partly melting the insulating material all small holes will be closed. An entrance of acid, which later on is used, is thereby obviated. In order to avoid also an influence of the'acid on the wires in the central hole, a drop of liquid insulating-material may be put on the cenered with a varnish, able to offer resistance against acid but preferably dissolvable in alcohol. After preparing the heating-body in this way the upper side of the same may acid in order, to dissolve the outer silver-cover of" the Wollaston wires, whereas the' inner very thin platinum-wire remains as the heatingconductor. Instead ofdissblving the silvercover of the wire, the same may be removed by an electrolytic process, as known in the v I v ineonirf art. In everycase the removal of the silvercover can take place only'at those parts of the Vollaston wires which lie free viz, which are not protected by the material of the insulating-block. These are in general the parts between the central holed and the outer holes 6. After finishing the treatment of the Wollaston wires the whole heating-bodyis dipped into alcohol in order to [0 remove the varnish, which formerly was arranged on the metahring for protection against the acid. Now the heating body is 'finished and may directly be used in a thermo-telephone in the known manner.

By arranging the central border 5 ona lower level than the outer border 2 all the very thin platinun1-wires-9, acting as heating-conductors, lie in a plane below the surface of the border 2 and therefore all wires are protected against damage.

and also the electric resistance of all heatingconductors is quite the'same. The number of heating conductors in'the heating body -may easily be varied as of course. a smaller number of wires may be used than holes 6 are provided.

The whole manufacture of the heatingbody and the treatment of the Wollastonwires is ver 1 simple and a deterioration of '30 the heating-conductors is impossible. In

the finished heating-body the metal-ring 10 forms the one pole and the knot 8 or another resistance in the center of the insulating-- block forms the other pole for the electric circuit. 7

I claim I i v 1. Inav heating-body for thermo-telephones the combination of an insulating block ha ing a central hole extending 40 "through the whole depth of said block and a number of holes near the periphery with a number of Wollaston wires, introduced .in

the central-hole and ray-like distributed to the outer holes and a contactpiece on the insulating block connected with the outer ends of the wires.

2. In a. heating body for thermo-tolcphones the combination of a insulating block of circular shape having a central hole extending through the whole depth of said block and a number of holes near the pcriphery with a number of IVoll'astcin wires, introduced in the central hole and rai -like distributed to the outer holes and a'contuctpiece on the insulating block connected with th outer ends of the wires.

3. In a heating body for thermo telcphones th combination of an insulatinnjblock having a. central hole surrounded by a border and a number of holes arranged in a border at the periphery of the block, the

outer border being higher than the central border, with a number of lVollaston wires, introduced in the central hole and ray-like distributed to the outer holes and a contactpiece on the insulating block connected with the outer ends of the wires.

4. In a heating-body for thernio-telephones the combination of an insulating block having a central hole and a number of holes near the periphery with a number of VVollaston wires, introduced in the central hole and ray-like distributed to the outer holes, and a metal-ring, arranged at the periphery of the insulatingblock, said metal-ring projecting below the lower sur--' face of the insulating-block and the lower part of this ringbeing in direct contactwith the lower and outer ends of the '01- 1 laston wires.

In testimony whereof I afli my signature in presence of two witnesses.

OTTO GRAETZER. Witnesses WOLDEMAR H AUPT,

IENRY HAsrnR. 

